Preston set his watch 15 seconds behind, and it falls behind another 10 seconds every day. how far behind is prestons watch if he last set it 4 days ago? write and solve and equation to find the answer

Hi, can anyone show me how to do this problem? 100 points for this. in advance

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Lizette is training for a marathon. at 7: 00 she left her house and ran until 8: 30, then she walked until 11: 30. she covered a total distance of 18 miles. her running speed was six miles per hour faster than her walking speed. find her running and walking speeds in miles per hour.